Mercurial Clients
The following is a brief description of some of the tools you can use to check code out from the Mercurial source control repository and to commit your changes. Some developers will already have their own favourite tool and some IDEs already have Mercurial plugins available, but others can charge a not inconsiderable fee for such a basic feature.
If you're unfamiliar with Mercurial, we also recommend Joel Spolsky's Hg Init website.
Integrated in your IDE
Mercurial support is available from a number of plugins for Visual Studio and other IDEs, and is on the MonoDevelop wish list.
HgEclipse is a great client that integrates well into Eclipse, but Eclipse does not support working with .Net languages.
External Mercurial clients
If your development environment doesn't include Mercurial integration then the only alternative is an external client. There are lots of clients for all OSes, or there's the classic fall-back of the command-line tools.
External GUI Mercurial Clients
The most popular client for Windows and Linux seems to be TortoiseHg. It can be used stand-alone or as part of your regular file browser on most desktops.
Mercurial from the command-line
The brave can always use Mercurial from the command-line. While it does have its uses, it's not generally advised for long-term use. Command-line arguments and usage instructions can be found in the Hg book at Red-bean.com.